Electrical switch



Dec. `1, 1953 f J. c. SHABECK, JR

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Dec. 1, 1953 Filed March 9, 1946 2r Z/ zo J. C. L. SHABECK, JR

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Patented Dec. l, 1953 2,661,408 ELECTRICAL SWITCH John C. L. Shabeck, Jr., Waltham,

Mass., assignor to United-Carr Fastener Corporation, Cambridge, Mass., a corporation of Massachusetts Application March 9, 1946, Serial No. 653,372

(Cl. 20D-76) 11 Claims.

The present invention relates to electrical switches and more particularly to switches wherein a movable contact member is moved to opened and closed position by a snap action and the invention aims generally to improve existing switches oi that type.

One of the primary objects of the invention is the provision of a snap switch possessing a large contact area, high contact pressure, large contact gap, maximum operating force acting in direction normal to the plane of the contacts, a high rate of contact opening and minimum mass and inertia of the movable Contact carrier which contribute to a minimum of contact bounce, thus increasing the serviceability of the switch under relatively heavy loads.

A further aim and object of the invention is the provision of a switch of novel construction and arrangement of parts that may be embodied in a unit of small size.

A still further object of the invention is the provision of a snap action switch of the direct impinging or abutting contact type that will possess improved operating characteristics under relatively heavy loads.

A still further object of the invention is the lprovision of an electrical switch the parts of which may be readily manufactured and asn sembled at a minimum cost.

Other aims and advantages of the invention will be apparent to those skilled in the art from a consideration of the following more detailed specification, reference being had to the accompanying drawings wherein:

Fig. 1 is a side elevation of the switch as viewed from one side;

` member;

Fig. 2 is a similar view as viewed from the po- Y sition at right angles to Fig. l;

Fig. 3 is an enlarged vertical longitudinal sectional vievv of the switch shown in'its open or circuit-broken position;

Fig. 4 is a similar view of the switch shown in its closed or circuit-making position;

Fig. 5 is a sectional view similar to Fig. 3, but taken at right angles thereto;

Fig. 6 is an enlarged outside side elevation of one section of the switch housing;

Fig. 7 is an edge elevation thereof;

Fig. 8 is a top plan view thereof;

Fig. 9 is an enlarged inside elevation thereof;

Fig. 10 is a horizontal sectional view taken on the line Ill- I0 of Fig. 9;

Figs. l1 to 14 inclusive are similar views taken respectively on the lines ll-ll to Ill-'I4 of Fig.

Fig. 15 is a fragmental vertical sectional view taken on the line IS-IE of Fig. 9;

Fig. 16 is a fragmental vertical sectional View taken on the line lli-IB of Fig. 6; l

Fig. 17 is a fragmental horizontalv sectional View taken on the line I'l--Ill 0f Fig.V 6

Fig. 19 is an edge view thereof;

Fig. 20 is an edge elevation of one of the xed contact members;

Fig. 21 is a front elevation thereof;

Fig. 22 is a top plan view of the operating yoke partly broken away better to illustrate the construction;

Fig. 23 is an edge elevation thereof;

Fig. 24 is a plan and edge view of the washer employed in the improved switch;

Fig; 25 is an edge and face elevation of the car rier employed therein; and

Fig. 26 is a plan and edge view of the grounding plate.

Electrical switches normally are designed and constructed for a predetermined load-carrying capacity. In many installations, for example in aircraft use, operating conditions vary so greatly that a switch having an adequate load-carrying capacity at or near ground levels will be inadequate at high altitudes.

For switches designed for relatively heavy loads contact area is an important consideration. For such uses switches of the direct impinging or abutting contact type are preferable to switches of the sliding contact type. According to the present invention direct impinging or abutting contacts are employed which have exceptionally large contact area which may be embodied in terminals of relatively heavy stock. This permits of the distribution of arcing erosion and the rapid dissipation of heat, imparting longer life and cooler operation to the switch.

However, switches of the direct impinging or abutting contact type are subject to contact bounce which, if permitted, causes arcing across the contacts and erosion of the contact surfaces. In cases where contact bounce is bad, the arc drawn across the contacts may be hot enough to cause welding of the contacts together. tact bounce is extremely critical when the switch is operating under an inductive load which induces a very high short voltage surge when current iiow is interrupted. For example, in certain solenoid operating circuits normally operating at 28 volts D. C., a voltage surge of 30D-400 volts is created across the switch contacts as current iiow is interrupted.

According to the present invention contact vbounce is substantially eliminated or reduced to a minimum by providing a maximum contact opening, a maximum operating force acting in a direction normal to the plane of the contacts, a high rate of contact opening and a minimum `mass and inertia of the movable contact carrier,

as will be more fully explained inthe following description of one suitable embodiment of the invention shown in the drawings.

Referring more particularly to the drawings,

Con-

the improved switch of the invention conveniently may comprise a housing which, for convenience, is advantageously formed of substantially semicylindrical complementary parts I and 2 preferably of molded insulating material, eacn of which may be formed with an upper operating mechanism cavity 3 and a lower contact cavity ii (Figs. 3 and 9) separated by a partition 5 having a central elongated aperture 6 therein.

The complementary housing parts I and 2 may be secured together in assembled position by suitable means, for example a rivet 1 extending through the housings I and 2 near one end thereof and an annular wire clamp or bail 8 seated in a peripheral groove En in the outer face of the housing I and 2 near the otherend thereof. The housing parts I and 2 may be formed with complementary locating means such as pins 3 and sockets 3a to insure proper alignment of the parts I and 2 when assembled together.

The contacts of the assembled switch are preferably Yof the direct impinging or abutting type, as distinguished from those which make and break contact by relative sliding movement. The contacts are formed of suitable 'conducting material such as coin silver and are mounted in the lower 'contact cavity and comprise a pair ol fixed contacts I mounted in laterally spaced relationship and an intermediate movable contact II (see Figs. 3 and 4). The contacts It and II are preferably formed of relatively thick `and heavy stock, having the capacity to dissipate heat created by any arcing', thus increasing the life and adding to the cooler operation of the switch.

The xed contacts I0 (see Figs. 2O and 2i) each comprise a substantially L-shaped bar adapted to be positioned in complementary recesses l2 molded in the supplementary housing sections I and 2 (see Figs. 9, 13 and 14). The 'iied contacts I have a relatively short arm I3 positioned transversely in the upper portion of the cavity d in spaced-apart relation and a substantially longer depending leg portion I4 extending downwardly through the recess I2( ahdbeyond the lower end of the housing members I and 2, the terminal ends of said leg portions being suitably formed as by being apertured atuIwto provide wiring terminals for connection with the respective leads of the circuit. The iixed contacts are securely maintained in position in the contact cavity 4 by means of angularly depending finge-rs I1 struck from the body of the legs I4 and bearing on angularly facing surface I8 in molded housings I and 2 (Fig. 13). The faces I3 are preferably inclined transversely as indicated in Figs. 9 and 15, so as to act on the fingers I1 and hold the upper arm portions of the fixed-contacts securely in the upper portions of the contact cavity 4.

It will be seen that the lower contact cavity t of each housing member comprises an interior chamber connected to the lower end of the housings by means of recesses I2 and an intermediate integral bottom for the cavity ll having inclined surfaces I8 for cooperative engagement oi the fingers I1. Thus the contacts may be inserted in one of the housing members I or 2 prior to assembly and are retained in their secured operative position by means of the fingers I1, permitting subsequent assembly with the other housing section therewith.

The provision of a switch having two spaced fixed contacts adapted to be bridged by a movable contact makes for a maximum contact opening or gap, eiectively doubling the gap without f it is desired to close the switch, which movable contact is secured to a carrier movable between the ends of the arms I3 of xed contacts and extending through the aperture e into the operating mechanism cavity 3. The movable contact i I advantageously is a. solid and continuous plate-like member having a reduced central portion 20 (see Fig. 18) and terminal portions 2i on opposite sides thereof, each adapted to make contact with its respective xed contact arm I3. The movable contact member I I is moved into and out of contact with the xed contacts I3 by means of a carrier disposed between and movable in a plane normal to the plane of the nxe'd contacts. The carrier is preferably of minimum mass and rweight so as to avoid as much as possible any tendency of contact bounce upon closing the switch.

In the illustrated embodiment the carrier 22 advantageously is of laminated construction comprising a metal conducting co-re 21 'fitted on opposite sides with insulating sheets 28 (see Fig. 3). The upper portion of the core 21 and insulating sheets 28 which are normally positioned in the operating mechanism cavity 3 are joined by means of a transverse metal eyelet 23 which not only secures the assembled core plate 21 and insulator sheets 28 together but provides a smooth walled opening for the operating spring later to be described. The carrier 22 is reciprocated in longitudinally extending guide channels 29 molded in the interior of the housing members I and 2 and opening into the cavities 3 and il (see Figs. 3, 9, 11 and 12). The carrier 22 is provided with an elongated opening 22a near its lower edge in which is movably mounted the contact II.

The carrier 22 with its associated movable contact II is movable longitudinally of the switch linto and out of contact with the spaced arms I3 by operating mechanism mounted in the operating mechanism cavity 3. Preferably the carrier is of a size and weight less than the operating mechanism so as to avoid tendency of the contact to bounce upon closing the switch. The cavity 3 of the complementary parts I and 2 is formed with an opening 30 for the operating button 3I and an inner enlarged cavity 3 for the operating mechanism, the inner portion of the cavity 3 being of reduced diameter and formed with guide channels 32 for guiding the reciprocable movements of a, yoke member 33. The yoke member 33 may be securely connected to the operating button 3| by means of a tubular rivet 34 molded into the button 3 I and having an end of the barrel upset over the bridge portion of the yoke as illustrated in Figs. 3 and 4. The tubular rivet 34 in the button 3I provides a housing for a return spring 35 bearing upon the end of the rivet and a disk or plate 3B xedly mounted in the operating mechanism cavity 3. As previously noted, the upper portion of the cavity 3 is advantageously of larger diameter than the portion containing the guide recesses 32 for the yoke, so as to provide shoulders 31 on which the disk 36 may be supported (see Figs. 3 and 9) `T'he lower ends of the yoke member are inturned to an acute angle lto the yoke sides as at 38 and are formed with reduced terminals 39 supporting the ends of an over-center toggle member or spring 'l0 which passes through the eyelet 23 and-serves to make and break the switch with a'snap action. Theacutely angled inturned yoke ends 38 andthe tapered terminals 39 thereof thus provide anti-'friction knife-edge support for the ends of the members l and thus reduce to a minimum resistance to movement of the member from one 'over-center position to an opposite position. Y

The spring Ill) may be of any form suitable for the purpose, but preferably i-s formed of a coiled compression spring of somewhat greater length than the distance between the inturned ends 38 of the yoke member '33, s o that it Will be bowed in its normal position. The switch, as stated, is

normally open or in circuit-broken position, with I' th movable contact in the lower portion 'of the cavity and the yoke raised to the upper portion of the cavity 3 by the return spring 35. In this position the inturned ends 38 of the yoke are in place above the center of the 'eyelet so that the normal position of the spring is concaved. When the circuit is closed, the spring is convexed as shown in Fig. 4,

The spring member 40 thus provides an overcent'er toggle device, the central portion of which is movable from its dead center 'compressed position to either 'the lower concav'ed position (Fig. 3) or the upper convex'ed position with a, snap action. Thus an exceptionally strong operating force is 'eiective to move'the movable contact Il and its carrier 22 in 'a direction normal to the plane of the movable and iixed contacts by the spring in compres-sion, when its center is displaced, resulting in remarkably high contact pressure between the contacts I Il-I I. This permits the switch to carry more current.

The operative connection between the spring 40 `and the movable contact carrier 22 is a smooth walled one, as presented by the tubular metal eyelet l23 and preferably has a working fit with the spring without appreciable lost motion. This is highly desirable in installations where the switch is to be closed upon a predetermined movement of the operating mechanism. The design of operating mechanism herein `shown insures operation of the switch within 11.0002" of a predetermined operational point, and when that operational point is reached (about .0001 beyond the dead center of the spring) the movable contact is moved into or out of engagement with 'the `fixed contacts with a swift strong snap action.

With the parts assembled as in Fig. 3 and the switch open or in circuit-broken position, depression of the button 3| acts to lower the operating yoke 33 and the terminal ends of the coil compression spring 40 at the same time compressing the return spring 35. When the ends of the yoke and the connected spring have been moved slightly past the central axis of the eyelet 23 (in the present case in its open position), the spring will snap to a bowed position opposite to that shown in Fig, 3 to a *convexed position shown in Fig. 4, thus raising the carrier'and movable contact with a snap action. This closes the circuit between arms I3 of the two iixed terminals I0. The switch will remain closed so long as the operating button is held depressed by the operator and, upon release of pressure on the button, the button Vis returned to its normal raised position by the action of the spring 35, thus raising the yoke 33. As the ends of the yoke and the coil spring 40 move past the axial center of the eyelet 23 in its raised position as shown in Fig. 4, the spring returns to the position shown in Fig. 3, thus moving the movable contact Il away from the terminal arms I3 by a snap action.

I prefer to have the contact member II so mounted in the carrier that it will make -a selflevelling floating contact with the xed terminal arms I3-'I3. This is accomplished by the slightly loose engagement of the notched edges 20 of the contact I I with the edges of the carrier 22 at the end-s of the opening 22a. This permits the contact II to rock or 'teeter and be self'- levelling to make equal contact under equal pressure with each of the xed contacts I0 and thus insure a maximum load-carrying capacity of the switch.

Furthermore, the ends 38 of the yoke 33 are preferably inclined so that pivot edges 38a--38 are presented to the ends of the spring "40 (Fig. 2'3). This arrangement permits the spring 40 to move more readily, from one position to the other, than would be the case if wider surfaces were brought to bear against the ends of the spring.

In certain types `of switches itis desirable to have an intermediate .grounded circuit and this may be simply and advantageously accomplished by my improved switch by merely making 'the disk 36 in the form 'of a grounding plate (see Fig. 26). The grounding plate in Fig'. 26 comprises a disk-like portion 36'a of a size and shape corresponding tothe disk 36 but with a wiring terminal flI extending therefrom and adapted to be inserted through an opening. This opening may be formed in the side wall 'of one of the housing sections l and 2 wherever convenient 'so that a wire may be connected thereto. The movable contact is then grounded through the metal carrier plate 22, the eyelet 23, spring Ml, yoke 33, tubular rivet 34, spring 35, washer 3'6a and wiing terminal 4I.

While other forms of `sprin'g devices lare contemplated within the scope of this invention, I prefer to use a coil over-center spring as this may be passed through a closely fitting aperture and then assembled 'with the operating yoke arms. Furthermore, 'such a coiled spring, under compression, exerts a maximum Yforce in a direction normal to the axis thereof, and exerts a greater contact pressure between the movable and xed contacts, thus enabling the switch to carry heavier electrical loads. It also is effective to eliminate iutter and contact bounce, permitting the movable contact to be ysupported directly by the carrier.

yOne of the advantages of the present invention is the provision of a mechanically operable switch mechanism that will be positive in its operation at all times and which `will not deteriorate by the action of an electric current flowing through it, as Yis the case with many existing switches or" this type.

Furthermore, the switch of the novel construction and arrangement of parts may be made in very small sizes, for example, with a casing of approximately one-half inch in diameter and less than one inch in length, which will be suitable to handle relatively heavy current loads at high altitudes without arcing. This is of particular advantage in connection with electric switch controls for aircraft.

The present application is a continuation-inpart of my prior copending application Serial No. 489,841, filed June 5, 1943.

I have chosen to illustrate the principles ro my invention in connection with the above illustrated form of switch, but it is understood that the theory of my invention could be applied to devices other than that specifically illustrated and described.

Although I have illustrated and described a preferred form of my invention, I do not wish to be limited thereby because the scope of my invention is best deiined by the following claims.

I claim:

l. An electric switch comprising a plurality of spaced fixed contacts, a relatively movable bridging contact adapted for direct impinging face-to-face contact with said fixed contacts, means for moving said movable contact in a direction normal to the plane of the xed contacts with a snap action between a circuit-making position and a circuit-breaking position comprising a movable contact carrier of less thickness than the spacing between said iixed contacts and movable therebetween and provided with a transverse opening, a helical over-center snap spring extended through said carrier aperture, a yoke bridging one end of the carrier and having arms spaced from opposite sides thereof for moving the opposite ends of said spring in one direction while said carrier is in one of said positions until said spring is moved through an axis of maximum stress whereupon said spring is caused to snap and move said carrier in an opposite direction by a strong snap action to its other selected position, fixed support means disposed between said carrier and yoke and spring means between said support means and yoke for moving the latter in one direction.

2. An electric switch comprising a plurality of spaced fixed contacts, a relatively movable bridging contact adapted for direct impinging face-to-face contact with said xed contacts, means for moving said movable contact in a direction normal to the plane of the xed contacts with a snap action between a circuit-making position and a circuit-breaking position comprising a movable contact carrier positioned between the xed contacts and movable in a direction normal to the plane thereof, said carrier having a transverse opening, a helical over-center spring extended through said carrier aperture, an operating member for the spring including opposed inturned spring end supporting means spaced from opposite sides of said carrier having free pivotal edge contacts with the end convolutions of said spring and restricted blade-like tongues inserted within the coil ends, and means for moving said operating member while said carrier is in one position to move the spring ends through an axis of maximum stress whereupon said spring is caused to snap in an opposite direction and move said carrier and movable contact relative to said fixed contact with a strong snap action, xed support means disposed between said carrier and yoke and spring means between said support means and yoke for moving the latter in one direction.

3. An electric switch having a plurality of spaced fixed contacts and a movable contact adapted to bridge pairs of said iixed contacts in circuit-closing position, and means for moving said movable contact between circuit-closing and circuit-breaking positions comprising an operating yoke, an over-center coiled spring operatively connected at its ends to said yoke, a movable contact carrier plate member of substantially less thickness than the length of said spring and disposed between said fixed contacts and normal to the movable contact and spring, said yoke being operable to move the ends of the spring in a direction normal to the plane of said fixed contacts past a dead center position to cause the central portion of the spring to be snapped be.. tween oppositely bowed positions and directly transmit to said carrier and movable contact the force of the spring under compression to maintain high pressure engagement between said movable and fixed contacts, said movable contact being freely rockable in said carrier to equalize the contact pressure of said spring between said movable and xed contacts, fixed abutment means between the carrier and yoke and spring means between said abutment means and yoke for urging said movable contact into one of said positions.

4. An electric switch having a plurality of spaced xed contacts and a movable contact adapted to bridge pairs of said fixed contacts in circuit-closing position, and means for moving said movable contact between circuit-closing and circuit-breaking positions comprising an operating yoke, an over-center coiled spring operatively connected at its ends to said yoke, a movable contact carrier plate member of substantially less thickness than the length of said spring and disposed between said xed contacts and normal to the movable contact and spring, said carrier having a transverse spring-receiving aperture having a working fit with said spring, said yoke being operable to move the ends of the spring in a direction normal to the plane of said fixed contacts past a dead center position to cause the central portion of the spring to be snapped between oppositely bowed positions and` directly transmit to said carrier and movable contact the force of the spring under compression to maintain high pressure engagement between said movable and fixed contacts, fixed abutment means between the carrier and yoke and spring means between said abutment means and yoke for urging said movable contact into one of said positions.

5. In an electric switch, a pair of xed contacts mounted in spaced relation, a longitudinally movable carrier for a movable contact disposed between said fixed contacts and movable between preselected switching positions, over-center snap spring means for moving said carrier between said preselected positions and maintaining it stable in one or the other of said positions, said carrier having an aperture extending through it providing aperture walls for surrounding said spring means, said spring means including a transversely deectable compressive spring whose axis of compression is substantially at right angles to the axis movement of said movable carrier and engageable with the aperture wallsv of said movable carrier, means for moving said compression element independently of the movement of said carrier through an unstable position of maximum coinpressionwhereupon said compression element is caused to snap in an oppositedirection and move said carrier with a strong `snap action to an opposite preselected switch position, said carrier comprising a core plate `of conducting material, insulating plates on opposite sides of said core plate and a tubular metal eyelet extending through all of said plates for securing said plates in assembled relation.

6. In an electric switch, in combination with a pair of fixed contacts mounted in spaced relation, a movable contact therefor, operating means for said movable contact including a carrier disposed between said iixed contacts and comprising a core plate of conducting material, insulating plates on opposite sides of said core plate providing means for insulating said core from said i-lxed contacts, and a tubular eyelet extending through all of said plates in assembled relation, and means passing through said eyelet for operating said carrier.

7. In an electric switch, in combination with a pair of xed contacts mounted in spaced relation, a movable contact therefor, operating means for said movable contact including a carrier disposed between said xed contacts and comprising a core plate of conducting material, insulating plates on opposite sides of said core plate providing means for insulating said core from said xed contacts, and a tubular eyelet extending through all of said plates for securing said plates in assembled relation, said eyelet being in electrical contact with said core plate.

8. An electric switch comprisilng a casing of insulating material formed with an operating mechanism cavity in one end thereof, a plurality of sets of guide grooves extending longitudinally,7 of said cavity, each of said sets dening a plane disposed at right angles to the planes of the other sets, a thin blade-like contact carrier reciprocably mounted in said casing with its opposed side edges disposed in one set of guide grooves, a U-shaped operating yoke having a bridge portion disposed transversely of said carrier and leg portions reciprocably mounted in the other set of guide grooves, an over-center spring member connected at its end portions to the ends oi said leg portions and extending through said carrier, fixed support means disposed between the said carrier and yoke and spring means between said support means and yoke for moving the latter in one direction, means for actuating the yoke member to move the ends of said spring past a dead center position of maximum stress to cause said spring to snap in an opposite direction, a fixed contact mounted in said casing and a contact member connected to said carrier and engageable with said xed contact.

9. An electric switch comprising a casing of insulating material formed with an operating mechanism cavity therein, and a restricted opening in one end of the casing communicating with said cavity, a portion of said cavity being of restricted diameter and formed with a pluralityT of sets of longitudinal guide grooves, each of said sets dening a plane disposed at right angles to the planes of the other sets, a thin blade-like contact carrier reciprocably mounted in one set of said guide grooves, an operating yoke having a bridge portion extending across said cavity and leg portions mounted in the other set of guide grooves, operative connections between said yoke and carrier, a plunger button secured to said yoke bridge and extending through said restricted casing opening, a disc member mounted in said cavity and supported on the outer end of the restricted portion thereof, and a spring member interposed between said disc and button.

10. An electric switch comprising a casing of insulating material formed with an operating mechanism cavity therein, and a restricted opening in one end of the casing communicating with said cavity, a portion of said cavity being of restricted diameter and formed with a plurality of sets of longitudinal guide grooves, each of ld said sets dening a plane disposed at right angles to the planes of the other sets, a thin blade-like contact carrier reciprocably mounted in one set of said guide grooves, an operating yoke having a bridge portion extending across said cavity and leg portions mounted in the other set of guide grooves, operative connections between said yoke and carrier, a plunger button secured to said yoke bridge and extending through said restricted casing opening, a disc member mounted in said cavity and supported on the outer end of the restricted portion thereof, a tubular eyelet embedded in said button and riveted to said yoke bridge and a return spring housed in said eyelet and bearing on said disc.

11. An electric switch comprising a plurality of spaced xed contacts, a longitudinally movable carrier of less thickness than the spacing between the spaced i'ixed contacts movable therebetween and in a direction normal to the plane thereof to preselected switching positions and comprising a plurality of insulating plates and a conducting metal core plate, a movable bridging contact mounted adjacent one end of said carrier and adapted to be moved thereby for direct impinging face-to-face contact in circuitmaking engagement with said xed contacts, said carrier provided with a transverse aperture spaced from said movable contact providing opposed spaced bearing faces, an over-center snap spring extended through said carrier aperture and having a working fit with the opposed bearing faces thereof, said movable carrier being of less thickness than the length of said coil spring, an operating yoke for said spring member having spring end supporting pivots normally disposed in a plane between the spring-engaging faces of said carrier aperture, and means for moving said yoke in a direction substantially parallel with said contact carrier to move the ends of said spring in one direction from a bowed condition in which the center portion of the spring has bearing engagement with one face of said carrier aperture through an axis of maximum stress thereof, to cause said spring to snap in the opposite direction into bearing engagement with an opposite face of said carrier aperture and move said carrier and movable contact relative to said fixed contacts with a snap action.

JOHN C. L. SHABECK, JR.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,207,097 Tregoning Dec. 5, 1916 1,575,179 Olley Mar. 2, 1925 1,762,075 Petersen June 3, 1930 1,790,974 Cox Feb. 3, 1931 1,808,348 Gatzsche June 2, 1931 2,121,079 Eskin June 21, 1938 2,125,432 Du Brie Aug. 2, 1933 2,198,474 Cook Apr. 23, 1940 2,200,995 Procter May 14, 1940 2,293,606 Kimbell Aug. 18, 1942 2,304,808 Draving Dec. 15, 1942 2,340,615 Rath Feb. 1, 1944 2,360,128 Hausler Oct. 10, 1944 2,432,581 Miller Dec. 16, 1947 2,473,970 Riche June 21, 1949 FOREIGN PATENTS Number Country Date 333,488 Germany Feb. 23, 1921 

